The Mabinogion
The most famous collection of Welsh literature in the Middle Ages, what is now known as The Mabinogion contains some of the earliest examples of Arthurian romances.
The Mabinogion contains eleven tales which may be split into three parts. The first four tales are what is known as The Four Branches of the Mabinogi, the second part contains three independant tales and the last three stories are Arthurian romances.
Online sources
Modern Edition
The Mabinogion
Usually referred to by the names of its translators Jones and Jones it generally considered to be the seminal English translation. The language of the translation itself can be a little stiff, and is in mock Shakespearian (ie, it uses thee's and thou's and -eth and -est suffixes). Contains a useful introduction.
The Mabinogion
Translated by Gwyn Jones and Thomas Jones
1949, Everyman (has had numerous reprints and updated editions)
Copyright Conrad Leviston (2000)